Generally, a drill bit is a key component of a drilling machine used to drill a rock by directly transmitting impact energy to the rock by percussion, rotation and feeding actions. FIG. 1 shows a drill bit having a diameter of 102 mm, and the drill bit has buttons 30 and flushing channels 40 arranged on a head.
When the buttons 30 of the drill bit are located at a new percussion position by the rotation, the percussion is performed. Also, the rock fractured by the percussion is fragmented again by consecutive percussion and rotation, and is discharged out of a drill hole by air supply.
FIG. 2(a) shows that the buttons 30 of FIG. 1 form four concentric circles (tracks). That is, button no. 1 hits the rock while drawing a circle (track) of radius r1 at the innermost, button nos. 2 and 3 hit the rock while drawing a second circle (track) of radius r2, and buttons nos. 4˜6 hit the rock while drawing a third circle (track) of radius r3. Finally, gauge buttons having nos. 7˜15 hit an outermost position while drawing a fourth circle (track) of radius r4.
In the process of drilling the rock, percussion spots of the buttons 30 change depending on operation conditions of a drifter. Although it is ideal for efficient rock drilling to operate a drifter to have overall uniform percussion spots, percussion spots of buttons overlap under a particular operation condition as in FIG. 2(b), causing drilling efficiency reduction. For reference, the percussion spots of FIG. 2(b) refer to spots for hitting the rock when the drill bit having the button arrangement of FIG. 2(a) operates at 180 R.P.M. (revolution per minute), 2200 B.P.M. (blow per minute), and it shows some overlap of percussion spots.
Because it is in reality impossible to operate the drifter to always have uniform percussion spots in construction site, it is important to arrange the buttons 30 to prevent an overlap of percussion spots.